Flask-cors

Fixes Issue 124 where only the first of multiple headers with the same name would be passed through.

**New Defaults**

1. New defaults allow all origins, all headers.

**Breaking Changes**

1. Removed always_send option.
1. Removed 'headers' option as a backwards-compatible alias for 'allowed_headers' to reduce confusion.

Would love to get some feedback to make sure there are no unexpected regressions. This should be backwards compatible for most people.

Update default options and parameters in a backwards incompatible way.

By default, all headers are now allowed, and only requests with an
Origin header have CORS headers returned. If an Origin header is not
present, no CORS headers are returned.

Removed the following options: always_send, headers.

Extension and decorator are now in separate modules sharing a core module.
Test have been moved into the respective tests.extension and tests.decorator
modules. More work to decompose these tests is needed.

* Adds logging to Flask-Cors so it is easy to see what is going on and why
* Adds support for compiled regexes as origins

Big thanks to michalbachowski and digitizdat!

This release fixes the behavior of Access-Control-Allow-Headers and Access-Control-Expose-Headers, which was previously swapped since 1.9.0.

To further fix the confusion, the `headers` parameter was renamed to more explicitly be `allow_headers`.

Thanks maximium for the bug report and implementation!

This is a bug fix release, fixing:
Incorrect handling of resources and intercept_exceptions App Config options https://github.com/wcdolphin/flask-cors/issues/84
Issue with functools.partial in 1.10.0 using Python 2.7.9 https://github.com/wcdolphin/flask-cors/issues/83

Shoutout to diiq and joonathan for reporting these issues!